1. Field of the Invention
This invention relates to valve position transmitters in general and more particularly to a valve position transmitter designed to preclude the misalignment of the transmitter during reassembly in the field--thereby precluding the improper designation of valve position, designed to facilitate the use of peripheral devices with the transmitter, and designed to minimize the damage to the transmitter resulting from the conditions in which it is used.
2. Description of the Prior Art
Valve position transmitters are known and are used to identify the relative operational position of a valve located in a separate valve assembly. Quite often valve position transmitters are utilized in hazardous environments to allow for the identification of a valve's position from a safe and remote distance. Furthermore, valve position transmitters are often used when the valve assembly itself is remotely situated and difficult to reach.
Existing valve position transmitters, however, are susceptible to misuse and damage. For example, it often becomes necessary during the course of regular maintenance to disassemble and reassemble a valve position transmitter in the field. Unless the valve position itself is checked at the time of reassembly and the system recalibrated, the valve position transmitter may be misaligned such that it identifies the wrong valve position. Such an error could have devastating effects. For example, the valve position transmitter disclosed in U.S. Pat. No. 4,494,566 provides for an indicator cover which may be placed upon the device in any of a number of different orientations. Accordingly, if during disassembly and reassembly of this device said cover is rotated ninety degrees without a corresponding change in the valve position, the result is a transmitter identifying a valve position opposite from that which actually exists.
Furthermore, as previously noted, valve position transmitters are often used in environmentally hazardous conditions wherein the corrosive effect on the device is substantial. In addition, repeated disassembly and reassembly of the device itself can result in wear and tear on the various elements of the device. Over the course of time this corrosion and this wear and tear can result in inaccuracies, or a total breakdown, in the device's ability to correctly identify a valve position. Again, this could cause problems in situations where an accurate reading is critical.
On occasion a valve position transmitter may be utilized with a peripheral device that is permanently coupled to the shaft portion of the transmitter. For example, one such device is a positioner. However, the permanent coupling of such a device to the transmitter shaft often times impedes the ability to conduct field work on the transmitter or its various components.
Finally, valve position transmitters often include a switch box assembly containing switches connected to other peripheral devices. Such switches may be used to signal the valve position to these peripheral devices. Again, the conditions under which valve position transmitter are used can cause deterioration of the switch box assembly. Furthermore, the relatively small size of the switch box assemblies may cause difficulties with respect to the field work required to be performed on the switches and their associated connections.